This invention relates to an improved roofing system. More particularly, this invention relates to an insulated, water impermeable roofing system for insulating the interior of a building from ambient thermal cycling and for insuring water impermeable integrity of a roof portion of the building.
The basic concept of a roof is to act in cooperation with generally vertical walls to form an enclosed space which may be isolated from an ambient environment and thus may be regulated in accordance with intended utilization.
A threshold or common denominator of almost all controlled environments is to maintain the enclosure in essentially a water tight or dry condition. Accordingly over the years the roofing industry, and particularly the commercial roofing industry, has attempted to maintain a water tight or water impermeable roof condition by building a water impermeable barrier, in situ, upon a roof substructure or deck. Such a water barrier has typically assumed the configuration of a laminar composite comprising a plurality of felt layers with intercalated courses of bituminous composition.
More particularly the bituminous compound typically arrives at a job site in solid cylinders. The cylinders are melted in a heater and the hot liquid is then carried in buckets to the roof deck where it is mopped onto a previously prepared roof substructure. A roll of felt paper is then carried to the roof and unrolled upon the hot bituminous compound which binds the felt to the roof deck. Three or more courses are then built up over the entire roof structure. The job is finished with a layer of topping gravel. The gravel weights down the felt courses and also serves as a shield to minimize ultra-violet degradation of the felt and bituminous membrane.
Although water impermeable roofing membranes, as previously noted, have been widely utilized in the commercial roofing industry substantial disadvantages have been occasioned. In this connection, elevated roof temperatures vaporize volatile components in the bituminous compound. The compound then tends to harden and crack in a checkered or "allegator" array. Moreover as the bituminous compound becomes hot during the summer months the overlay course of gravel tends to sink into the membrane. Further, prior roofing systems often developed vapor blisters, splitting or ridging.
The above factors each tended to create water seepage difficulties which ultimately rendered the roof unsuitable for its intended purpose.
In addition to water impermeability considerations conventional environmental control criteria dictates internal isolation from thermal cycling which takes place at the exterior surface of a roof. More particularly the exterior surface of a roof may experience temperatures during midsummer as high as 180.degree. while a winter cold front may drop the temperature to as low as 20.degree. or 30.degree. below zero. The interior surface of the roof, however, should optimally be maintained at a desired interior temperature which typically is 65.degree. to 75.degree. Fahrenheit.
In order to provide thermal protection an initial practice entailed lining the interior surface of the roof with an insulation composition such as sprayed or layered glass fibers, fiberboard, plastic foams and the like. While such insulation facilitated the thermal cycling problem it severely accentuated the previously outlined difficulties occurring with the felt and bituminous water barrier by, in essence, isolating the barrier from the relatively stable interior temperature of the building structure. Accordingly it was not uncommon for roof membranes to require considerable attention and in some instances periodic replacement.
A significant advance in the roofing art occurred in the relatively recent past when it was determined that an insulation course could be effectively installed exterior of the felt and bituminous water barrier. The thus positioned insulation still provided a building with isolation from thermal gradients as desired while at the same time protected the felt and bituminous waterproofing barrier.
An insulated roof membrane assembly which has attained at least a degree of industry recognition comprises a water barrier of felt and bituminous lamination which is built up, in situ, in a manner as previously discussed. A hot course of bituminous compound is then mopped upon the final layer of felt and generally rectangular panels of polystyrene are laid directly upon the hot bituminous compound. The polystyrene insulating members are mutually abutted against each other, however, a peripheral fissure inherently exists between the members and permits water to drain thereinto and away from the upper surface of the roofing insulation. A relatively heavy course of aggregate is loosely applied directly upon the upper surface of the thermal insulating members to hold the members in place and isolate the insulation surface from ultra-violet degradation.
While such a system, as previously noted, has achieved at least a degree of industry recognition and utilization, room for significant improvement remains.
In this regard, an insulated roof membrane assembly as described in the proceeding requires on site fabrication which is laborious, hot and extremely odorous. Accordingly it is sometimes difficult to obtain and retain qualified personnel to install the system. Moreover the loose gravel which is applied directly to the insulation course in order to maintain it in place is typically deposited at a rate of 1,000 pounds per square foot or more. The roof deck must therefore be designed to support a considerable amount of weight. Still further, since the aggregate is applied in a loose condition, it is not recommended to apply the foregoing roofing system to a roof having a pitch any greater than 2/12. Additionally, during rains, water collects in the insulation fissures which drains along the waterproofing membrane and serves to strikingly reduce the insulation effectiveness. Yet further, because of the exposed character of the insulation panels the types of insulations which may be utilized are limited to only those which will not be damaged during installation by a layer of hot bitumen and which are relatively incapable of absorbing water and/or are not water degradable. Moreover, because water is designed to channel within the fissures if the weight aggregate is in some manner displaced, the individual panels are subject to floatation. Additionally, it is difficult or cumbersome to roll or push equipment upon the loose aggregate and thus it is somewhat difficult to utilize the roof as a service entrance. Still further, it is difficult, if not impossible, to apply the above noted insulated roof membrane to all the different varieties of roof deck structures which now exist in the roofing industry, such as, for example, corregated metal roofs.
The problems suggested in the proceeding are not intended to be exhaustive, but rather are among many which may tend to reduce the effectiveness of prior insulated roofing membrane assemblies. Other noteworthy problems may also exist; however, those presented above should be sufficient to demonstrate that insulated, water impermeable roofing systems appearing in the prior art have not been altogether satisfactory.